Molecular defects in beta-thalassaemias in the population of Saudi Arabia.

The beta-thalassaemias are a heterogeneous group of inherited disorders caused by mutations in and around the structural gene of the beta-chain of the adult haemoglobin (HbA). Studies at the gene level have identified a large number of beta-thalassaemia gene variations in different populations. These findings have implications for the use of molecular diagnosis for genetic counselling and prenatal detection of the beta-thalassaemias. In our unit, we initiated studies to investigate the molecular defects in beta-thalassaemias in Saudi Arabia using amplification-refractory mutation systems, dot blot analysis and restriction endonuclease analysis, and identified mutations producing beta(+)- and beta zero-thalassaemias. Twenty of the mutations encountered in the Asian, Mediterranean, Chinese and other Arab populations were investigated. The most commonly encountered mutations in Saudi beta-thalassaemia patients were IVS-I-110, IVS-II-1, CD 39, IVS-I-5 and IVS-I 3' end (-25), while frameshifts at CD 8/9, Cap+1 (A-->C) and CD 6 mutations were identified at a low frequency. These mutations account for 84.94% of the total beta-thalassaemia mutations. The remaining 15% remain unknown. This is the first report on the type and nature of mutations in Saudi beta-thalassaemia patients. It presents frequencies of twenty mutations and emphasises the need for further detailed investigations to clarify the whole spectrum of beta-thalassaemia mutations in the Saudi population.